The Global System for Mobile Communications (GSM), known as a Second Generation (2G) digital mobile cellular communication system, has been commonly applied worldwide. Due to the scarcity of frequency resources and the increasing demands for new services, the trend of development is turning to the Third Generation (3G) mobile communication system and the Beyond Third Generation (B3G) mobile communication system inevitably. In the existing 3G system and B3G system, a non-constant envelope digital modulation system is commonly used to obtain a sufficient signal bandwidth. The use of this modulation technology not only facilitates the acquisition of a high rate signal, but also brings about a stricter requirement upon the linearity of a base station transmitter including a power amplifier.
In the prior art, one solution to the linearity of a power amplifier in the 3G system or the like is a feed forward scheme. However, this scheme may be disadvantageous because the use of analogy technologies results in a high complexity in implementation of this scheme and a poor consistency in manufacturing procedures, as well as precise adjustment for various parameters of a feed-forward network required for a professional technician. Moreover, a large number of additional analogy radio frequency devices are needed in the implementation of the method, so the efficiency of the power amplifier can not be improved effectively.
In the prior art, another solution to the linearity of a power amplifier in the 3G system or the like is a method for pre-distorting a base-band digital signal. The essence of this method is to feed back a signal output from the power amplifier to the digital domain in a certain way, then to calculate the linearity characteristic of a radio frequency channel including the power amplifier by using an adaptive algorithm, and finally to preprocess the base-band digital signal by a pre-distorter before converting the signal from the digital domain into the analogy domain. The preprocessed signal passed through the power amplifier approximately presents no distortion compared with the base-band digital signal. As a result, a linear output from the power amplifier is achieved.
This pre-distortion method may be disadvantageous in that the nonlinear function of the pre-distorter can not be selected according to different applications. In other words, this method has to be designed according to specific applications, and hence can not be applied universally. As a result, the transmitter of a base station may have a relatively low efficiency as a whole.